The present invention relates to thin keyboard switches and, in particular, to a thin keyboard switch whose key stem moves up and down smoothly when the key is struck at its edge rather than at its center.
Generally, a conventional thin keyboard switch has an upper printed circuit board, an insulating spacer, and a lower printed circuit board. The pair of printed circuit boards and the insulating spacer are stacked like a sandwich on an insulating base. A pair of contacts, one fixed, and one moveable, attached respectively to the upper and lower printed circuit boards face each other within a cavity in the insulating spacer. On the upper printed circuit board sits a housing above which a key top is attached by an elastic coupling such as a coil spring.
A key stem is attached to the underside of the key top. The center of the key stem is a sliding body that slides within a guiding body shaped as a cylindrical shell with a space through its center. Fastening portions under the key top engage fastening portions outside the guiding body to limit the travel of the key.
When this conventional key is struck at its edge, it does not move smoothly. It may in fact catch, bind, or stick in its travel up and down. The conventional key catches, binds, or sticks because the distance of vertical key travel is smaller than the horizontal distance between the points about which the key top rocks if it is struck at the edge. That is, when the key is struck at its edge rather than at its center, a moment is created that adds a rotational component to the key's downward motion. (The point through which this moment acts will hereinafter be called the "moment point".)